Catalytic converter heating

ABSTRACT

The rate at which a catalytic converter heats up to its normal operating temperature range, (e.g., during a start up phase) is increased by applying an external load to an internal combustion engine. Applying the external load causes the engine to generate more heat, which can be used to reduce the time that it takes to bring the catalytic converter up to its working temperature. As a result, a reduction in emissions can be achieved.

BACKGROUND OF THE INVENTION

A significant proportion of the emissions from a modern automotiveinternal combustion engine occurs during the first few minutes of engineoperation following a cold start. This is due to the catalytic converternot being able to function correctly until it achieves “light off”; thatis, until it has reached its working temperature.

A catalytic converter can be very effective at reducing unwanted exhaustemissions when it is operating at its working temperature. However,until a catalytic converter reaches its working temperature, it isworking inefficiently at best. As a result, untreated exhaust gas canexit the end of the exhaust or tail pipe. In the first two to threeminutes of warm-up following a cold start, about 60% to 80% of exhaustor tail pipe emissions occur.

The regulatory authorities are imposing ever more strict emissionregulations. In order to provide an effective reduction in exhaustemissions, it is therefore desirable to cause the catalytic converter toreach its working temperature as quickly as possible.

Various approaches have been employed to reduce the time that it takes acatalytic converter to reach its working temperature. One approach is tomove the catalytic converter as close to the exhaust port as possible.Another approach is to provide electrical and/or flame heaters forcatalytic converters. A further approach is to provide an exhaust gascombustion system. Yet a further approach is to provide a mechanism toretain the heat in a catalytic converter between engine operations. Allof these approaches involve expensive modifications to an existingengine system and/or exhaust system and/or provide packaging challenges.

Other engine based approaches include providing precise fueling control,providing controlled ignition retarding, providing secondary airinjection, using high starting engine speed and providing changes to thecatalyst physics. These approaches include various disadvantagesincluding a less enjoyable driving experience (e.g. due to increasednoise), reductions in performance, complexity, combustion instabilityand cost.

Accordingly, there is still a need for an effective solution to reducethe time it takes for a catalytic converter to reach its workingtemperature.

BRIEF SUMMARY OF THE INVENTION

The invention may be embodied in a method of operating an engine systemthat includes an internal combustion engine operable to apply drive to adrive train, a catalytic converter through which exhaust gases from theinternal combustion engine pass, and a control system. In an exampleembodiment, when the control system determines that the internalcombustion engine is in a phase in which the catalytic converter isbelow its working temperature, it causes an external load to be appliedto the internal combustion engine. By applying an external load, theengine generates more heat, which can be used to reduce the time that ittakes to bring the catalytic converter up to its working temperature. Asa result, a reduction in emissions can be achieved.

The invention may also be embodied in an engine system that includes aninternal combustion engine operable to apply drive to a drive train, acatalytic converter through which exhaust gases from the internalcombustion engine pass, and a control system. The control system, inresponse to a determination that the internal combustion engine is in aphase in which the catalytic converter is below its working temperature,can cause an external load to be applied to the internal combustionengine. A motor vehicle can be provided with such an engine system.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of this invention, will be morecompletely understood and appreciated by careful study of the followingmore detailed description of the presently preferred exemplaryembodiments of the invention taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a chart illustrating an example of emissions during phases ofoperation of an engine system;

FIG. 2 is a chart illustrating accumulated emissions during operation ofan engine system;

FIG. 3 is a schematic representation of a motor vehicle including anengine system;

FIG. 4 is a schematic representation of an engine system;

FIG. 5 is a schematic representation of the operation of an enginesystem in normal running;

FIG. 6 is a chart showing various parameters of the engine system duringnormal running;

FIG. 7 is a schematic representation of the operation of a prior artengine system in a start up phase;

FIG. 8 is a chart showing various parameters of the prior art enginesystem of FIG. 7 in a start up phase;

FIG. 9 is a schematic representation of the operation of an exampleengine system in accordance with the invention in a start up phase;

FIG. 10 is a chart showing various parameters of the example enginesystem of FIG. 9 in a start up phase;

FIG. 11 is an example of an engine system in accordance with theinvention in which an external load is applied through a torqueconverter;

FIG. 12 is an example of an engine system in accordance with theinvention in which an external load is applied through a crankshaftbrake;

FIG. 13 is a chart comparing an example of catalytic convertertemperatures over time;

FIG. 14 is a chart illustrating an example of an improvement in theincrease of catalytic converter temperature over time; and

FIG. 15 is a chart showing various parameters of an engine system andconsequent reduction in total fuel consumption in an example embodimentof the invention.

DETAILED DESCRIPTION OF THE INVENTION

An example embodiment of the invention seeks to increase the rate atwhich a catalytic converter heats up to its normal operating temperaturerange by applying an external load to an internal combustion engine whenthe catalytic converter is below its working temperature, in order toreduce the time that it takes to bring the catalytic converter up to itsworking temperature. As a result, a reduction in emissions can beachieved.

Examples of phases of operation of an internal combustion engine inwhich a catalytic converter may be below a desired operating temperaturerange can include a start up phase, after a water splash or immersion inwater, and in the case of a hybrid vehicle, during a phase in whichpower is taken from batteries rather than the internal combustionengine. The external load can be applied in different ways as willbecome apparent from the following description.

FIG. 1 is a chart illustrating an example of emissions during phases ofoperation of an engine system that includes an internal combustionengine. More specifically, FIG. 1 illustrates an example of theemissions of an internal combustion engine, for example a gasolineengine, over time from a cold start. As can be seen in FIG. 1, in thecircled phase after start up, high emissions are seen.

FIG. 2 represents the accumulated emissions of gases such ashydrocarbons (HC), nitrogen oxides (NO_(x)) and carbon dioxide (CO₂). Itcan be seen from the charts in FIGS. 1 and 2 that a significantproportion of the undesired emissions occur during the early start upphase. This is the phase before the catalytic converter has heated up toits normal operating temperature range and in which the catalyticconverter is ineffective or at least less effective that optimum. Thetime that the catalytic converter takes to get up to its normaloperating temperature range is often called the “light off time”.

FIG. 3 is a schematic representation of a motor vehicle 10 including anengine system 12 according to an example embodiment of the invention. InFIG. 3 the motor vehicle is an automobile and the engine system includesan internal combustion engine 14 with a drive train 16 driving thedriven wheels 18. In the present example, the vehicle 10 has rear wheeldrive. However, it will be appreciated that in other examples frontwheel drive or all wheel drive can be provided. In the present examplethe drive train 16 is understood to include the transmission 20. Thetransmission 20 in the present example is an automatic transmission witha torque converter, although in other examples a manual transmission oran electronically controlled manual transmission could be provided.

FIG. 4 is a schematic representation of an example of an engine system12 in more detail. As shown in FIG. 4, the internal combustion engine 14is provided with an air intake system 22 and an exhaust system 24including an exhaust pipe or tail pipe 23. The exhaust system 24includes a catalytic converter 25 for processing the exhaust gases. Acontrol system 26 includes an engine management controller 28 that isresponsive to various sensors, including one or more lambda probes 30,one or more catalytic converter temperature sensors 32, and one or moreambient temperature sensors 34, one or more crankshaft sensors 36, etc.In an example embodiment, the control system is also operable to controlthe automatic transmission 20, braking systems (not shown in FIG. 4) andother systems as well as controlling engine parameters such as ignitiontiming, fuel injection timings and so on.

FIG. 5 is a schematic representation of the operation of an enginesystem during normal running. FIG. 5 represents, schematically, theinternal combustion engine 14, the engine output shaft 42 (e.g. thecrankshaft, an extension thereof, or a further shaft driven by thecrankshaft), the transmission 20, including a torque converter 44 and agearbox 46 (or in the case of a manual transmission, a clutch 44 and agearbox 46), and a transmission drive shaft 48.

FIG. 6 is a chart that represents, schematically, for the engine systemof FIG. 5, the conditions of various parameters including engine load,ignition retard, engine speed, throttle, external load and heat flux tothe catalyst during normal running. It will be appreciated that FIG. 6represents these conditions in a steady state situation. It will also beappreciated that in normal use, these parameters can be changed, forexample during acceleration, deceleration, etc.

FIG. 7 is a schematic representation of the operation of a prior artengine system during a start up phase. FIG. 7 represents, schematically,the internal combustion engine 14, the engine output shaft 42 (e.g. thecrankshaft, an extension thereof, or a further shaft driven by thecrankshaft), the transmission 20, including a torque converter 44 and agearbox 46 (or in the case of a manual transmission, a clutch 44 and agearbox 46), and a transmission drive shaft 48.

FIG. 8 is a chart that represents, schematically, the conditions ofvarious parameters including engine load, ignition retard, engine speed,throttle, external load and heat flux to the catalyst during an exampleof operation of the prior art engine system of FIG. 7 during a start upphase. FIG. 8 illustrates that at an activation point, variousparameters are changed. Specifically, it will be noted that afterignition (where the ignition trace drops) the throttle is increased,which also increases the engine speed and engine load caused by internalengine factors such as friction, etc. As a result, heat flux to thecatalytic converter increases to start to heat the catalytic converter.Once again, it will be appreciated that FIG. 8 is schematic and is forillustrative purposes only.

FIG. 9 is a schematic representation of the operation of an exampleembodiment of an engine system in accordance with the invention during astart up phase. FIG. 9 represents, schematically, the internalcombustion engine 14, the engine output shaft 42 (e.g. the crankshaft,an extension thereof, or a further shaft driven by the crankshaft), thetransmission 20, including a torque converter 44 and a gearbox 46 (or inthe case of a manual transmission, a clutch 44 and a gearbox 46), and atransmission drive shaft 48. FIG. 9 also illustrates, schematically, theapplication of an external load to the engine output shaft 42,symbolized by hand 50. It will be appreciated that the representation ofa hand 50 in FIG. 9 is merely to illustrate the effect of applying anexternal load in accordance with example embodiments of the presentinvention. In practice the load is not provided by a hand, but rather bytechnical features of the engine system and/or the motor vehicle, asdescribed in greater detail below.

FIG. 10 is a chart that represents, schematically, the conditions ofvarious parameters including engine load, ignition retard, engine speed,throttle, external load and heat flux to the catalyst during an exampleof operation of the engine system of FIG. 9 during a start up phase.FIG. 10 illustrates that at an activation point, various parameters arechanged. Specifically, it will be noted that after ignition (where theignition trace drops) the throttle is increased by a greater amount thanin the prior art example of FIG. 8, although the engine speed onlyincreases by the same amount as in the prior art example of FIG. 8. Thisis because an external load is applied (see the lower circled portion inFIG. 10), which means than the overall engine load is increased more(see the upper circled portion in FIG. 10) than in the prior art exampleof FIG. 8. This is turn means that there is a greater heat flux to thecatalytic converter (see the lower circled portion in FIG. 10) than inthe prior art example of FIG. 8. Once again, it will be appreciated thatFIG. 10 is schematic and is for illustrative purposes only. However, acomparison of FIGS. 8 and 10 can illustrate the effect of applying theexternal load to increase the heat flux to the catalytic converter andhence to reduce the light off time for the catalytic converter.

The external load can be applied until the catalytic converter hasreached a predetermined temperature, for example a minimum efficientoperating temperature, for a predetermined time, or a combinationthereof (for example until it reaches the predetermined temperature oruntil a predetermined time has elapsed, which ever occurs first). Aswill be seen in FIG. 14 later, a significant benefit can be realizedthough the use of the applied external load within the first ten secondsof operation. Accordingly, the external load could be applied merely fora predetermined period, for example twenty seconds, or ten seconds, orfive seconds. The choice of a particular duration of the load can alsobe dependent upon the amount of the loading that is applied. In general,the higher the loading, the shorter the time, although the loadingshould not be set such that it exerts excessive strain on the engineduring the start up phase.

FIG. 11 is an example of an engine system in which an external load isapplied through a torque converter. More specifically, FIG. 11 is aschematic representation of a front engined, rear wheel drive vehiclewhere drive from the engine 14 is supplied via an automatic transmission20 that includes a torque converter 44 and gears 46 to a drive shaft 48.The drive shaft 48 is then connected via a differential 52 and secondarydrive shafts 54 to the rear wheels 18. In the example shown in FIG. 8,an electrically operated parking brake 60 is provided that is used whenthe vehicle is stationary.

In operation of the engine system shown in FIG. 11, the control system26 is operable to detect the activation point illustrated in FIG. 10following ignition. This can be detected, for example, when ignition isachieved following a cold start of the engine or a start when thecatalytic converter is below its normal operating range of temperatures.The control system 26 is then operable automatically to engage a drivengear (either forward or reverse) while at the same time engaging theparking brake. The brake 60 could be configured as a friction brakemember that engages a secondary drive shaft 54. In the present example,an electrically operated friction brake is used, although in otherexamples other forms of operation could be used. Also, the brake couldbe in the form of a visco-mechanical coupling, an eddy current brake, aregenerative braking system, or indeed any other suitable form of brakethat can apply a controllable braking force. This has the effect of theholding the torque converter still via the drive train. This in turncauses an external load to be applied to the engine over an above thenormal loading caused by internal friction, etc., which means that theengine generates more heat for a given engine speed. The control system26 can be operable to maintain the engine speed at a desired level togive smooth running under load by applying an appropriate amount ofthrottle. The result of applying the additional external load is thatthe light off time for the catalytic converter can be reduced comparedto a prior art engine where an external load is not applied.Alternatively, the additional external load can enable the same amountof heating compared to a prior art engine where an external load is notapplied, but at a reduced engine speed. A further advantage of provingthe external load via the gearbox is that also reaches a normaloperating temperature more quickly, reducing consumption due to reducedfrictional losses.

FIG. 12 is an example of an engine system in which an external load isapplied through an engine output shaft brake. More specifically, FIG. 12is a schematic representation of a front engined, rear wheel drivevehicle where drive from the engine 14 is supplied via a manualtransmission 20 that includes a clutch 45 and gears 46 to a drive shaft48. Although a manual transmission is shown in FIG. 12, an automatictransmission could be provided instead. The drive shaft 48 is thenconnected via a differential 52 and secondary drive shafts 54 to therear wheels 18. In the example shown in FIG. 12, the engine output shaftthat connects the engine to the clutch 45 is provided with anelectrically operated engine output shaft brake 62. The brake could belocated outside of the engine casing, or it could be included within theengine casing and could act, for example, on a crankshaft of the engine.

In operation of the engine system shown in FIG. 12, the control system26 is operable to detect the activation point illustrated in FIG. 10following ignition. This can be detected, for example, when ignition isachieved following a cold start of the engine or a start when thecatalytic converter is below its normal operating range of temperatures.The control system 26 is then operable automatically to apply a brakingforce to the engine output shaft using the engine output shaft brake 62.The brake force that is applied is set such that it is not sufficient tostop the engine from turning over, but is merely enough to apply anexternal loading to the output shaft. The brake 62 could be configuredas a friction brake member that engages the output shaft. In the presentexample an electrically operated friction brake is used, although inother examples other forms of operation could be used. Also, the brakecould be in the form of a visco-mechanical coupling, an eddy currentbrake, or indeed any other suitable form of brake that can apply acontrollable braking force. This effect of the applied braking force isto cause an external load to be applied to the engine over an above thenormal loading caused by internal friction, etc., which means that theengine generates more heat for a given engine speed. The control system26 can be operable to maintain the engine speed at a desired level togive smooth running under load by applying an appropriate amount ofthrottle. The result of applying the additional external load is thatthe light off time for the catalytic converter can be reduced comparedto a prior art engine where an external load is not applied.Alternatively, the additional external load can enable the same amountof heating compared to a prior art engine where an external load is notapplied, but at a reduced engine speed.

FIG. 13 is a chart comparing an example of catalytic convertertemperatures over time with and without the application of an externalload. The upper curve 70 illustrates the heating of the catalyticconverter with the externally applied load and the lower curve 72illustrates the heating of the catalytic converter without theexternally applied load.

FIG. 14 is a chart illustrating an example of an improvement in theincrease of catalytic converter temperature over time. FIG. 14illustrates the surprising result that within the first ten seconds ofthe order of a 50% to 100% improvement in the increase in temperaturecan be achieved with the use of the external load compared to notapplying the external load.

FIG. 15 illustrates various parameters of an engine system and anexample of a reduction in total fuel consumption, or at least re-gain ofthe extra fuel used during the initial catalytic heating phase duringlater phases of operation of the internal combustion engine. Morespecifically, as illustrated by the schematic accumulated fuelconsumption chart of FIG. 15, initially fuel consumption could beslightly higher due to the application of an external load, although notnecessarily since the prior art mode needs rich to run stable. However,as illustrated, the accumulated fuel consumption is possibly improved(reduced) or at least the initially higher consumption is re-gained dueto rapid coolant and gear box heating, as schematically shown, whichreduces the total friction loss, as also schematically shown. Theinitially higher consumption is depicted in the circled area in the leftof the accumulated fuel consumption chart whereas the improved/reducedfuel consumption is illustrated in the circled section in the right ofthe accumulated fuel consumption chart.

Thus there has been described a method and apparatus that can increasethe rate at which a catalytic converter heats up to its normal operatingtemperature range by applying an external load to an internal combustionengine during a phase in which a catalytic converter is below a desiredoperating temperature range. Applying the external load generates moreheat that can be used to reduce the time that it takes to bring thecatalytic converter up to its working temperature. As a result, areduction in emissions can be achieved.

Example embodiments can be applied to vehicles having drive trains withmanual and with automatic transmissions.

In one example with an automatic transmission having a torque converter,a drive mode is engaged with the torque converter immobilized. In oneexample the torque converter can be immobilized by applying a parkingbrake, for example an electrically operated parking brake. In otherexamples, the torque converter could be immobilized in other ways, forexample by incorporating an additional brake in the gearbox, or byapplying the vehicle's hydraulic braking system. As a further example,the braking could be applied using a regenerative braking system, forexample in a hybrid vehicle. Through the use of a regenerative brakingsystem, electrical energy could be generated and stored, for example ina battery or fuel cell, while still providing the advantage of theadditional loading and more rapid catalytic converter heating.

Another example that can be used with manual and automatic transmissionsuses an engine output shaft brake that is used to apply an external loadto the engine output shaft, for example to the crankshaft of the engine.The external load in the form of a braking force can be applied indifferent ways; for example using an electrically controlled crankshaftor engine output shaft brake, a visco-mechanical coupling, etc.

In the above description, reference has been made to engine systemshaving manual transmissions and automatic transmissions with a torqueconverter. It will be appreciated that embodiments of the inventioncould be applied to other engine systems having other transmissionssystems, for example a continuous variable transmission (CVT).

The external load can be applied using different approaches including,by way of example only, hydraulic braking systems, electrically operatedbraking systems, adaptive cruise control systems, regenerative brakingsystems, visco mechanical couplings, etc.

An embodiment of the invention can be operable to provide the externalload during a phase of operation of the internal combustion engine whenthe catalytic converter is below its normal operating temperature range.Such phases of operation can include, by way of example only, a start upphase (e.g., following a cold start), a restart phase (e.g., following atemporary stop in traffic), a post-splash phase (e.g., followingsplashing or immersion of the catalytic converter in water), an electricdrive phase (e.g., in operation of a hybrid vehicle when drive ispowered by a battery rather than the internal combustion engine).

Although the embodiments above have been described in considerabledetail, numerous variations and modifications will become apparent tothose skilled in the art once the above disclosure is fully appreciated.It is intended that the following claims be interpreted to embrace allsuch variations and modifications as well as their equivalents. Thus,while the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1. A method of operating an engine system, the engine system includingan internal combustion engine that is operable to apply drive to a drivetrain, a catalytic converter through which exhaust gases from theinternal combustion engine pass and a control system, the methodcomprising: determining whether the internal combustion engine is in aphase in which the catalytic converter is below its working temperature;and causing an external load to be applied to the internal combustionengine when the internal combustion engine is in a phase in which thecatalytic converter is below its working temperature.
 2. The method ofclaim 1, wherein the external load is applied to the drive train.
 3. Themethod of claim 2, wherein the drive train includes an automatictransmission having a torque converter and wherein to apply saidexternal load, the control system is operable to engage a drive modewith the torque converter immobilized.
 4. The method of claim 3, whereinto immobilize the torque converter, the control system is operable toapply a parking brake.
 5. The method of claim 4, wherein the parkingbrake is controlled electrically.
 6. The method of claim 1, wherein thecontrol system causes an external load to be applied to an engine outputshaft.
 7. The method of claim 6, wherein the engine output shaft is acrankshaft of the engine and wherein the control system causes a brakingforce to be applied to the crankshaft.
 8. The method of claim 7, whereinthe braking force is applied by an electrically controlled crankshaftbrake.
 9. The method of claim 7, wherein the braking force is applied bya visco-mechanical coupling.
 10. The method of claim 1, wherein theexternal load is applied for a predetermined period.
 11. The method ofclaim 1, wherein the external load is applied until the catalyticconverter reaches a predetermined temperature.
 12. An engine systemcomprising: an internal combustion engine that is operable to applydrive to a drive train, a catalytic converter through which exhaustgases from the internal combustion engine pass, and a control system,wherein the control system is operable to determine when the internalcombustion engine is in a phase in which the catalytic converter isbelow its working temperature; and to cause an external load to beapplied to the internal combustion engine.
 13. The engine system ofclaim 12, wherein the control system is operable to cause the externalload to be applied to the drive train.
 14. The engine system of claim13, wherein the drive train includes an automatic transmission having atorque converter, and wherein the control system, in order to applyexternal load, is operable to engage a drive mode of the transmissionand to immobilise the torque converter.
 15. The engine system of claim14, wherein the control system, in order to immobilise the torqueconverter, is operable to apply a parking brake.
 16. The engine systemof claim 15, wherein the parking brake is controlled electrically. 17.The engine system of claim 12, wherein the control system is operable tocause an external load to be applied to an engine output shaft.
 18. Theengine system of claim 17, wherein the engine output shaft is acrankshaft of the engine, and wherein the control system, is operable tocause a braking force to be applied to the crankshaft.
 19. The enginesystem of claim 18, comprising an electrically controlled crankshaftbrake for applying the braking force.
 20. The engine system of claim 18,comprising a visco-mechanical coupling for applying the braking force.21. A motor vehicle comprising an engine system, the engine systemcomprising an internal combustion engine that is operable to apply driveto a drive train, a catalytic converter through which exhaust gases fromthe internal combustion engine pass, and a control system, the controlsystem being operable to determine when the internal combustion engineis in a phase in which the catalytic converter is below its workingtemperature; and to cause an external load to be applied to the internalcombustion engine.